Seems to be a pretty direct translation (without reading the sources of both).
Now, if they took the original source and used it to implement a grammar then based the rust code off said grammar they might have a case -- which, I believe, is what a "clean room" implementation would do, preferably with two different people doing either task.
IMHO this is a clear copyright violation else you could just "reimplement" your way out of any license.
